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A Modem Sharing Device (MSD), also commonly known as a Line Sharing Device (LSD), modem sharer, or line sharer, allows multiple devices to share a serial connection. Only multipoint serial protocols such as bisync are supported. Both synchronous and asynchronous datastreams can be used. A common example would have a Tandem as host connected to multiple Automatic Teller Machines often with a modem or Ciscorouter in-between.
